Target delineation in many cancers is required when employing intensity modulated radiation therapy (IMRT). Methods to identify targets for delineation typically rely on volumetric imaging (e.g., computational tomography (CT), magnetic resonance (MR), positron emission topography (PET)) combined with non-volumetric imaging such as physical exam findings and endoscopy. At times, endoscopy and physical exams reveal areas of visible or palpable tumour extension which are not clearly demonstrated on volumetric imaging. However, interpreting endoscopy images as it relates to the volumetric imaging may be subject to error. This may be at least partly because localizing disease usually relies on remembering the relationship of the disease to fixed anatomic landmarks that are visible on both the volumetric imaging and endoscopy, which, by its nature, may be imprecise or inaccurate.
Radiotherapy planning is becoming more and more conformal, leading to concern that a tumor may be unintentionally ‘missed’ during the planning process and a desire to accurately delineate tumors during the planning process. One method of addressing this is to use relatively large planning margins to minimize the risk of missing tumors. However, using large margins to minimize this risk is associated with increased risk of morbidity and late side-effects. Ideally, one would like to limit the treatment to the tumor and avoid normal tissue as much as possible. Recent research has suggested that high quality radiation therapy (including proper identification of target) can be associated with a survival advantage. Of course, identifying the target is a useful important step in treatment of any malignancy1.
In patients with endoluminal malignancies, including, for example, head and neck, esophagus, bronchial, lung and lower gastrointestinal cancers, it is well accepted that the physical examination plays a critical role in determination of the ‘target’ for radiation therapy. Often, physical exam findings can reveal areas of visible or palpable tumor extension which are not clearly demonstrated on volumetric imaging studies. Using indirect fiberoptic endoscopy visualization of the nasopharynx, oropharynx, and larynx, for example in head and neck cancers, can reveal subtle changes which alter the target that will be planned for radiation treatment. Variations on standard white light endoscopy can also be used to improve target delineation. Narrow band imaging2 and autofluorescence3 endoscopies have demonstrated increased sensitivity in determining the extent of disease, although at a cost in specificity. The combination of all of these has been shown to improve, for example, the early diagnosis of esophogeal disease such as Barrett's esophagous, and would possibly improve diagnosis in head and neck cancer as well4. This combination has also been found to be useful in other cancers, including, for example, lung and colon cancers. At present, the visual information available during endoscopy cannot be directly (or quantitatively) used in the planning process, rather, the clinician ‘interprets’ (i.e., qualitatively evaluates) the physical exam findings relative to the available volumetric planning data to create a ‘composite’ target. This usually requires reliance on relationships to anatomic landmarks or structures which are visible on CT and endoscopy.